As it happens my office is right next to a sewage farm, so I can tell you that they only stink a couple of days a month. It depends where in the process they are. So you could check it out several times and still be unlucky on the day. That's interesting about the embankment, though. I'm not sure if our one has one (it's at 52.233319, 0.155565). Do you have information that it's to reduce the smell, or were you assuming that that's why you couldn't smell anything when you went?